LM2671N-ADJ National Semiconductor, LM2671N-ADJ Datasheet - Page 17

• Manufacturer Part Number: LM2671N-ADJ
• Description: Voltage Regulator IC
• Manufacturer: National Semiconductor

Specifications of LM2671N-ADJ

• Output Current: 500mA
• No. Of Pins: 8
• Peak Reflow Compatible (260 C): No
• Leaded Process Compatible: No
• Mounting Type: Through Hole
• Package / Case: 8 Lead
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

where V
V
B. Use the E • T value from the previous formula and match it
with the E • T number on the vertical axis of the Inductor
Value Selection Guide shown in Figure 7 .
C. On the horizontal axis, select the maximum load current.
D. Identify the inductance region intersected by the E • T value
and the Maximum Load Current value. Each region is identified
by an inductance value and an inductor code (LXX).
E. Select an appropriate inductor from the four manufacturer’s
part numbers listed in Figure 8 . For information on the different
types of inductors, see the inductor selection in the fixed
output voltage design procedure.
3. Output Capacitor SeIection (C
A. Select an output capacitor from the capacitor code selection
guide in Figure 16 . Using the inductance value found in the
inductor selection guide, step 1, locate the appropriate
capacitor code corresponding to the desired output voltage.
B. Select an appropriate capacitor value and voltage rating,
using the capacitor code, from the output capacitor selection
table in Figure 17 . There are two solid tantalum (surface
mount) capacitor manufacturers and four electrolytic (through
hole) capacitor manufacturers to choose from. It is
recommended that both the manufacturers and the
manufacturer’s series that are listed in the table be used. A
table listing the manufacturers’ phone numbers is located in
Figure 11 .
4. Catch Diode Selection (D1)
A. In normal operation, the average current of the catch diode
is the load current times the catch diode duty cycle, 1-D (D is
the switch duty cycle, which is approximately V
largest value of the catch diode average current occurs at the
maximum input voltage (minimum D). For normal operation,
the catch diode current rating must be at least 1.3 times
greater than its maximum average current. However, if the
power supply design must withstand a continuous output short,
the diode should have a current rating greater than the
maximum current limit of the LM2671. The most stressful
condition for this diode is a shorted output condition.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
C. Because of their fast switching speed and low forward
voltage drop, Schottky diodes provide the best performance
and efficiency. The Schottky diode must be located close to
the LM2671 using short leads and short printed circuit traces.
LM2671 Series Buck Regulator Design Procedure (Adjustable Output)
D
(Continued)
= diode forward voltage drop = 0.5V
PROCEDURE (Adjustable Output Voltage Version)
SAT
= internal switch saturation voltage = 0.25V and
OUT
)
OUT
/V
IN
). The
17
B. E • T = 21.6 (V • µs)
C. I
D. From the inductor value selection guide shown in Figure 7 ,
the inductance region intersected by the 21.6 (V • µs)
horizontal line and the 500 mA vertical line is 100 µH, and the
inductor code is L20.
E. From the table in Figure 8 , locate line L20, and select an
inductor part number from the list of manufacturers’ part
numbers.
3. Output Capacitor SeIection (C
A. Use the appropriate row of the capacitor code selection
guide, in Figure 16 . For this example, use the 15–20V row.
The capacitor code corresponding to an inductance of 100 µH
is C20.
B. From the output capacitor selection table in Figure 17 ,
choose a capacitor value (and voltage rating) that intersects
the capacitor code(s) selected in section A, C20.
The capacitance and voltage rating values corresponding to
the capacitor code C20 are the:
Surface Mount:
33 µF/25V Sprague 594D Series.
33 µF/25V AVX TPS Series.
Through Hole:
33 µF/25V Sanyo OS-CON SC Series.
120 µF/35V Sanyo MV-GX Series.
120 µF/35V Nichicon PL Series.
120 µF/35V Panasonic HFQ Series.
Other manufacturers or other types of capacitors may also be
used, provided the capacitor specifications (especially the 100
kHz ESR) closely match the characteristics of the capacitors
listed in the output capacitor table. Refer to the capacitor
manufacturers’ data sheet for this information.
4. Catch Diode Selection (D1)
A. Refer to the table shown in Figure 12 . Schottky diodes
provide the best performance, and in this example a 1A, 40V
Schottky diode would be a good choice. If the circuit must
withstand a continuous shorted output, a higher current (at
least 1.2A) Schottky diode is recommended.
LOAD
EXAMPLE (Adjustable Output Voltage Version)
(max) = 500 mA
OUT
)
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